Thus it came to pass that when the king set out, before Dernhelm sat Meriadoc the hobbit, and the great grey steed Windfola made little of the burden; for Dernhelm was less in weight than many men, though lithe and well-knit in frame.
There are no more uses of "lithe" in the book.
Show samples from other sources
The lithe dancers seem to float across the stage.
Although Elvis is best known for his lithe, gyrating "Hound Dog" days, it is his later, weightier, gold lamé–draped self that remains the most emulated among most of his impersonators.
Alyssa Fetini -- Time Inc, 2010 -- http://www.time.com/time/specials/packages/article/0,28804,1952461_1952460_1952463,00.html#ixzz0wPA0qwrx(retrieved 08/12/10)